Inject Default Values Safely with $request->mergeIfMissing() - Laravel

Use $request->mergeIfMissing() in Form Requests to set default fallback parameters without overwriting user-provided values.

When handling search queries, pagination limits, or optional boolean flags, calling $request->merge() overwrites existing values.

mergeIfMissing() injects default parameters only when the key is absent from the request payload.

Using mergeIfMissing in Form Requests

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class FilterProductsRequest extends FormRequest
{
    protected function prepareForValidation(): void
    {
        $this->mergeIfMissing([
            'per_page' => 15,
            'sort'     => 'latest',
            'status'   => 'active',
        ]);
    }

    public function rules(): array
    {
        return [
            'per_page' => ['integer', 'min:1', 'max:100'],
            'sort'     => ['in:latest,price_asc,price_desc'],
            'status'   => ['in:active,archived'],
        ];
    }
}

Summary

Sets fallback values only when keys do not exist in the request.
Preserves explicit user inputs (including false or 0).
Keeps validation rules and controller actions clean and predictable.

Tags: Laravel HTTP Form Requests Clean Code

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